Field of the Invention
The present invention relates generally to prosthetics with a hydraulic damper or actuator. More particularly, the present invention relates to a prosthetic ankle.
Related Art
The development of a prosthetic ankle with a more natural function or gait is an ongoing endeavor. Examples of prosthetic ankles include U.S. Pat. No. 6,443,993 (Koniuk); U.S. Pat. No. 2,843,853 (Mauch); and U.S. Pat. No. 7,985,265 (Moser).
Prosthetic ankles can incorporate a hydraulic damping scheme to limit or control movement about the ankle, and/or to allow limited range of motion for the foot to provide a natural gait on slops or inclined surfaces. The hydraulic damping systems often utilize a solenoid valve to limit or resist the flow of hydraulic fluid. A solenoid valve is typically on or off, and can typically operate by drawing a plunger into an activated magnetic coil and against a spring, which spring can return the plunger when the coil is deactivated. In addition, some hydraulic damping systems may also, or in the alternative, utilize a stepper motor. Furthermore, some hydraulic damping systems can utilize a magneto rheological fluid. Alternatively, some hydraulic damping systems can utilize mechanical controls.
In addition, side loads are commonplace in prosthetic devices. Side loads cause, at a minimum, premature failure of hydraulic cylinder seals, and at the worst, binding or bending of the cylinder components, especially the shaft. The typical approach to eliminate side loads on a hydraulic cylinder is to mount it with spherical ball joints (also known as Heim joints) at both ends. In this way, side loads are not transmitted to the cylinder because the spherical ball joints move to accommodate the side loads. In prosthetic devices, using spherical ball joints can be impractical because this greatly increases the eye-to-eye length of the cylinder, but the cylinder must fit within the anatomical envelope of a natural leg. For this reason, most prosthetic devices that employ a hydraulic cylinder have the cylinder mounted on trunnions. But trunnions will transmit side loads.
Prior art prosthetic ankles often do not meet the advanced demands needed by today's amputee.